Magnetic amplifier dimmer



May 3l, 1960 R. VRAQENBURGH 2,939,050

MAGNETIC AMPLIFIER DIMMER Filed Oct. 19, 1956 INVENTOR. /'aas/w- Moen/5006# United States Patent O MAGNETIC AMPLIFIER DIMMER Robert Vradenburgh, Yonkers, N.Y., assignor to Ward Leonard Electric Co., Mount Vernon, N.Y., a corporation of New York Filed Get. 19, 1956, Ser. No. 617,155

8 Claims. (Cl. 315-278) The invention relates to variable output voltage circuits and apparatus and is directed particularly to the supplying of an output voltage over a range in a given predetermined relationship with a range of input control voltages irrespective of the value of the output current at each voltage.

In electrical apparatus providing an output voltage, the output voltage varies with the output current provided by the apparatus. It is often desirable to vary the output voltage over a range of values in response to a range of input control voltages with each output voltage corresponding to an input voltage and at each Ivoltage to provide a range of .currents depending on the load. The purpose of this .invention is to provide compensating means to maintain =each output vol-tage constant over the range of current so :that each output voltage will correspond to a particular input voltage irrespective of the amount of current supplied at that particular output voltage.

This invention is particularly applicable to the reimote control of a plurality of incandescent lamps. In

the remote control of groups or banks of lamps, the operating characteristic of the control apparatus changes with loads of different Wattage ratings. A given setting of the apparatus will produce different degrees of illumination of a single element `depending on the total wattage of all elements. It is preferable that a given setting of the input control will cause the same output voltage to be impressed across each load unit, irrespective of the number of elements so loaded.

An object of the invention is to provide an electrical apparatus for delivering a range of currents at each output voltage of a range of output voltages with the particular output voltage remaining constant over the range of currents.

Another object of the invention is to provide an electrical apparatus having a lrange of output voltages corresponding to a range of input control voltages, irrespective of the current provided at each output voltage.

A further object of the invention is to provide an electrical apparatus for supplying a range of output voltages to a load in accordance with a range of input control voltages with the relationship of output voltages and control voltages independent of the wattage of the load.

A still further object of the invention is to provide lamp illumination control apparatus inwhich the intensity of illumination of each lamp of a plurality of lamps corresponds with a given value of input control, irrespective of the number or total number of lamps connected to the output of the apparatus.

Other and further objects of the invention will be apparent from the following detailed description taken in connection with the drawings in which:

Fig. l is a diagrammatic view of the circuit.

Figures 2 and 3 are charts of the performance of the apparatus. In this embodiment the load 10 may comprise one or (more incandescent lamps of high wattage. The lamps 'may be used for lighting stages or other types of areas re quiring a high degree of illumination that may be varied over a wide range. The purpose of this apparatus is to control this high wattage load by means of asmall, low wattage control 11 such as a rheostat in the order of two watts. 'Ille current supplied to the lamps -10 is regulated primarily by means of control 11; magnetic amplier stages 12 and 13` may have a capacity from 5-40 kw. depending upon the power requirements of the particular installation. The output of stage 13 is connected to the load 10 -by line 48. The amplifier stage 12 controls the output of the second stage 13 and is in turn controlled by the control device 11. The control device 11 is adjusted through a range of voltages. Each voltage position corresponds to a particular degree of illumination of each lamp of the load. This voltage is constant at each setting and has a linear relationship with the voltage at the lamps. The number of lamps or the total wattage of the load may be changed and the total load current for a particular setting may change, but the illumination of each individual lamp will remain essentially the same. in order to maintain the output voltage of stage 13 constant at a particular input voltage, a corrective signal is impressed on stage 12 which is related to the voltage impressed across the load 10, resulting in a corrective signal for providing voltage linearity between control and output voltage and having characteristics to be dened later resulting in essentially constant output voltage at all control settings irrespective of the magnitude of the connected load. This corrective signal, is created by a feedback proportioning circuit or unit 34 and comprises a specially designed reactor and rheostat.

In Fig. 1, a detailed schematic diagram is shown of the dimming system. The stage 12 comp-rises a magnetic amplifier having two saturable reactors 22 and 23 with anode windings 22a and 23a connected -to the power lines 24a and 24E-b, with rectiiiers 25 and 26 connected in series with a respective anode winding and an output rectifier 27 for providing a D.C. output current.

The bias windings 22b and 23th are provided with a direct current from the bias circuit 28 which is connected to a suitable direct current supply (not indicated) by lines 28a, 2811. The resistor 29 is connected. across the lines 28a, ZSb and has an adjustable contact 29a for setting the bias current in accordance with fthe magnetic amplifier characteristics desired. A resistor 30 is provided in series with the bias windings to limit the current to the windings to a predetermined maximum value.

The windings 2.2i and Zf are connected in series to the output of the feedback circuit 31 connected to the load. The feedback circuit 3-1 is connected to the rheostat 47 in the feedback proportioning circuit 34 to provide a corrected feedback signal of the proper value.

The output of the feedback proportioning circuit 34 corrects the ampliiication characteristics of stage 12 to compensate for variations in the characteristics of stage 13 with different values of load. Thus, with a steady D.C. voltage impressed across potentiometer 32 and the correction provided by the feedback proportioning circuit 34, the illumination of each lamp of the load 10 will correspond with a definite setting the contact 32a irrespective of the number of lamps in the load and the current drain on stage' 13. The characteristics of the feedback proportioning circuit further determine the variation of the output voltage as related to control input voltage. The values of the components of the feedback proportioning circuit may ybe set to provide strict voltage linearity between input and output voltage or to provide strict linearity between potentiometer 32 and candle power output of the lamps.

The feedback proportioning circuit, therefore, has two primary functions. One function is to determine the relationship of the variation of the output load `voltage `varying load conditions.

to the input control voltage and the other is to determine the deviation of the output voltage for a particular input control voltage for different values of load current supplied to the lamp 10. .'In the operation of the control system, the magnitude of the exciting current carried by the reactor 46 and the slope of the magnetization curve of the reactor 46 determine Vthe value and variation of the voltage appearing across the rheostat 47, at all points of the magnetization curve of the reactor, to provide feedback control to windings 22 and 23)c properly proportioned to provide effective control of the input vs. output characteristics. The reactor 46 operates over the linear portion of its current-voltage characteristic.

A In the diagram of Fig. 2, the line A indicates the ideal or optimum linearity relationship between the output load voltage and the input control voltage for optimum impedanoe characteristics of the feedback proportioning circuit. Lines D and E illustrate the dimmer curve for maximum and minimum load current with zero inductaance the feedback proportioning circuit. At the full control voltage, the output voltage between maximum and minimum load current is 13%, as indicated by the distance I. The lines B and C indicate the maximum deviation of the output load voltage for a particular input -control voltage over the maximum range of load current at that particular setting. At the maximum input control voltage the difference between the maximum current and the minimum current is 4%, as indicated by the distanke K. Thus, by including the reactor 46 in the feedback proportioning unit a 70% correction is attained in .the deviation.

The adjustment of the impedance of the reactor varies the magnetization current and the voltage drop across the voltage resistor 47 in a manner that provides properly proportioned voltage changes for control of the feedback current in stage 12. The changes in feedback in this manner will` effect changes in stage 12 output which in turn will effect changes in stage 13 output and have a material effect on the output voltage characteristic as related to control voltage at 32. In this manner the input vs. output characteristic can be adapted to a variety of Vrequirements such as strict linearity between input and output voltage, strict linearity between control potentiometer 312 position and output voltage, and strict linearity between control voltage and candle power merely by adjusting the impedance of reactor 46.

Fig. 3 shows the effect on the characteristic of dimmer output voltage vs. control voltages for two dilferent reactors of different impedances. For purposes of illustration, curve F shows the effect of the reactor 46 with a value of impedance selected to cause the characteristic of dimmer voltage vs. control voltage to elevate above true voltage linearity line H by approximately the same amount that the typical dimmer curve G with zero impedance is depressed below true voltage linearity line H. Also for illustration, line H shows the effect of the reactor 46 with a value of impedance selected to cause the characteristic of dimmer voltage vs. control voltage to fall approximately midway between dimmer curve F and the dimmer curve G wherein the inductance in circuit 34 is zero. Line H is an acceptable dimmer voltage vs. control voltage characteristic if true voltage linearity is to be desired. Other dimmer voltage vs. control voltage characteristics could be obtainable by further changes in impedance of the feedback proportioning circuit.

The second main function of the feedback proportioning circuit 34 is to correct dimmer voltage output under Fig. 2 illustrates the effect on the dimmer curve of adding optimum impedance in the feedback proportioning circuit for maximum and minimum load conditions as compared with the dimmer curve using the same loads but with Zero impedance in the :feedback proportioning unit. As previously explained, the correction in output voltage deviation at the maxilmum input control voltage, by adding optimum impedance in the feedback proportioning circuit, is approximately 70%. This corrective effect is also apparent over the dimming range, although not to the same degree. The feedback proportioning circuit forms a filtering means to reduce the harmonics of the voltages across the components of the feedback proportioning circuit from which the `feedback voltage is derived. This characteristic appears to provide the desired correction in dimmer voltage for maximum and minimum load conditions. The correction in wave shape and the reduction'in ripple in the D.C. output of the full wave bridge rectifier 39 results in an improved feedback to the stage 12, which produces changes in the output of stage 13 in the same manner as previously described.

Circuit 31 rectiiies the alternating current by means of the full wave bridge rectifier 39 and provides a lead network for anti-hunt and filtering purposes by means' of the elements 53 and resistor 54. The windings 22u and 23C are connected in series to the low wattage control 11. The control 11 comprises a potentiometer 32 connected across a low voltage, direct-current supply in the order of 6 to 20 volts. The amount of voltage impressed across the windings 22C and 23C is determined vby the adjustable contact 32a. This contact determines the degree of intensity of illumination of the lamps in the load it). The higher the voltage across the windings 22C and 23C, the greater the degree of illumination that will be made by the lamps 10. A resistor 33 is connected in series with the control windings 22C and 23e. The D.C. voltage impressed across the potentiometer 32 should preferably be very steady so that the lamps will not change in illumination at a given setting of the contact 32a.

The alternating output of stage 12 is connected to the stage 13 through the rectiiier 27 and the resistor 38. T he Ystage 13 comprises a magnetic ampliier having saturable reactors 40 and 41, each comprising a three-legged core. The output of the rectier is supplied to the control windings 40c and 41C of the reactors 40 and 41 respectively to impress thereon a direct-current control for adjusting the output of the stage 13. The reactors are biased by the direct current supplied by the rectifier 55 connected to the supply lines. The anode windings 40a and 41a are connected in parallel between the A.C. power lines 24a and 24h, and have rectifiers 42 and 43 connected in series with the windings 40aV and 41a respectively to pass direct current through each winding and provide an alternating current output from the stage 13. iConnected in parallel across the rectiiiers 42 and 43 are resistors 44 and 45, respectively. The line 48 is connected between the rectiers 42, 43 to supply the alternating load current to the lamp 10 and the feedback proportioning circuit 34. As previously described the reactor 46 of the feedback proportioning circuit controls the current through the rheostat and the voltage across the rheostat. The voltage is tapped by the variable contact 47a and supplied to the rectifier '39 of the feedback circuit.

Various modifications and changes may be made in the apparatus without departing from the invention as set forth in the appended claims.

I claim:

l. In combination with an amplifying apparatus having an input control means for controlling the output voltage and current of said amplifying apparatus and a feedback circuit for controlling the amplmcation factor of said amplifying apparatus, a reactor and a resistor connected in series across the output having the output voltage impressed thereacross, said reactor having a linear current-voltage relationship to pass a given current through said combination reactor and resistor for a given output voltage and having means connecting said resistor to said feedbackcircuit for impressing a voltage on said amplifying apparatus to maintain the amplification factor of said amplifying apparatus constant on occurrence ofconditions tending to alter the ampliicationfactor `of said amplifying apparatus so that a linear relationship is maintained between the input control voltage and the output voltage over the entire range of output voltages and currents supplied by said amplifying apparatus.

2. In combination with an amplifying apparatus having an input control means for controlling the output of said amplifying apparatus and a feedback circuit for controlling the amplification factor of said amplifying apparatus, a reactor and a resistor connected in series across the output and having the output voltage impressed thereacross, said reactor having a linear current-voltage relationship to pass a given current through said combination reactor and resistor for a given output voltage and having means connecting said resistor to said feedback circuit for impressing a voltage on said amplifying apparatus that corresponds to a particular output voltage, comparative means in said amplifying apparatus for maintaining the gain of the amplifying apparatus constant when conditions tend to alter the output voltage from the desired output voltage corresponding to a particular input control voltage thereby maintaining a substantially linear relationship between the input control voltage and the output voltage over the entire range of voltages and currents supplied by said amplifying apparatus.

3. A dimming apparatus for supplying an incandescent lamp load and comprising an amplifier having an input control means providing an input control voltage over a range of values and an output for supplying current to an incandescent lamp load, said amplifier having a feedback circuit, said feedback circuit including a reactor and a resistor in series connected across the output for supplying an incandescent lamp load to have the output load voltage impressed thereacross, said reactor having a linear current-voltage characteristic to pass a given current through said resistor for a particular output load voltage and said feedback circuit including electrical means connecting said resistor to said amplifier to impress on said amplifier a signal relating the output load voltage to the gain of the amplifier for maintaining a substantially linear relationship between the input controlvoltage and the output load voltage so that for each setting of the input control voltage the lamps will have a predetermined intensity of illumination.

4. A dimming apparatus as set forth in claim 3 in, which said amplifier comprises an input magnetic amplifier and an output magnetic amplifier connected to and controlled by said input amplifier wherein said first magnetic amplifier has a three-legged core with a control winding wound on the mid-leg of said core and a second winding is provided connected to said feedback winding to provide a iiux corresponding to a given output load voltage to vary the gain of the first stage and thereby maintain the input and output voltages in substantially linear relationship.

5. A dimming apparatus as set fonth in claim 4 wherein said feedback circuit has filtering means to reduce the harmonics in said feedback signal for reducing the variation from a linear relationship between the input and output voltages.

6. An incandescent lamp dimming apparatus comprising amplifying means having an output for supplying an alternating current to an incandescent lamp load, control means connected to said amplifying means for supplying an output control voltage to said amplifying means through a given incremental sequence to control the amplification of said amplifying means, a feedback circuit connected to said amplifying means for controlling the gain thereof and having a series reactor and resistor combination connected across the output supplying the incandescent lamp load, said reactor having an inductance with a linear current-voltage characteristic in order to pass a given current for a given output load voltage to provide a feedback voltage on said resistor corresponding to the output load voltage, said feedback circuit impressing on said amplifying means a feedback voltage corresponding to the output voltage to maintain the amplification gain of said amplifying means constant and thereby maintain a substantially linear relationship between said input control voltage and said output load voltage.

7. Apparatus for `supplying power to a load over a range of voltages and currents in response to an input control voltage and comprising control means for produring a control voltage adjustable over a range, an input magnetic amplifier connected -to said control means and having an output responsive thereto, an output magnetic amplifier connected to said input magnetic amplifier and having an output for supplying alternating current to a load, a feedback circuit connected to said input magnetic amplifier and having a reactor and a resistor connected in series across the output supplying the load and having the output voltage impressed thereacross, said reactor having a linear current-voltage relationship to pass a given current through said combination reactor and resistor for a given load voltage, said feedback circuit impressing a signal corresponding to the current through said resistor on said input magnetic amplifier to alter the amplification factor of said input magnetic amplifier to compensate for changes in the amplification of the output magnetic amplifier so that a linear relationship is maintained between the input control voltage and the output control voltage over the entire range of voltages and currents supplied by said output magnetic amplifier.

8. An apparatus for supplying an output voltage to a load utilizing a range of voltages and currents which create a variation in the output voltage comprising an amplifier having an output supplying a load and an input control means providing an input control voltage over a range of values to produce a corresponding amplified range of output voltages, a feedback circuit including a reactor and a resistor in series connected across said output for impressing the output load voltage thereacross, said reactor having a linear current voltage characteristic to pass a given current through said resistor for a particular output load voltage, said feedback circuit connected to said amplifier for impressing on said amplifier a. signal to maintain the gain of the amplifier constant when the output current tends to vary the gain of the amplifier and hereby maintain a substantially linear relationship between the input control voltage and the output load voltage so that for each setting of the input control voltage a corresponding output load voltage is impressed thereacross irrespective of the load conditions.

Logan Apr. 27, 1937 Arvidsson Jan. 5, 1954 

